The present invention relates to a new and improved highly accurate, low power low speed fuze oscillator contained in a fast moving projectile which contains a programmable projectile fuze.
The timing accuracy requirement for modem projectiles is on the order of .+-.0.1% over wide climatic conditions in order to obtain a high probability of kill on the desired target and to limit undesired damage to adjacent structures or personnel. In a short-barrel/high-speed/high-accuracy weapon, the time between set-back and muzzle exit (when timing should start) is typically only 2 to 3 msec. In addition, set-back imposes an acceleration stress of 30,000 to 60,000 g's on the fuze.
Pyrotechnic devices have been used extensively in the past, but are unable to attain the required accuracy, especially over temperature extremes.
Analog timing circuits have also been used. While they are more accurate than pyrotechnic devices, they also have trouble in reliably meeting the stated accuracy.
Digital count down circuits have, for the most part, replaced other approaches. The primary contributor to accuracy error is the oscillator used to clock the digital circuits. Crystal oscillators can easily provide the accuracy required, but suffer from a typical start up period of several to tens of microseconds and have trouble surviving the high g environment (30,000 g to 60,000 g) in a reliable manner.
On the other hand, ceramic resonators are bulk devices that can readily take the high g environment and, also, can start up ten times faster than crystals. However, their accuracy is poor. They have tolerances of about .+-.0.25% individually for set, temperature drift and aging (which together results in an SRSS error of about .+-.0.43%). Also, ceramic oscillators can not be used at frequencies below about 80 kHz.
RC oscillators exist in the prior art for use at frequencies below 80 kHz, but none are available that can meet the accuracy requirements over temperature while drawing only 10 to 20 uA from the power bus.
Therefore, no previously known prior art involving low speed oscillators provides a frequency accuracy of .+-.0.1% over a wide temperature range while drawing low power, quick start-up, and can survive a high g environment in a reliable manner.